The invention relates to a pyroelectric detector with an optimized quality, efficiency or merit factor. It is applicable to the field of pyroelectric detection and more particularly to that of infrared imaging and detection. These processes use generally monocrystalline dielectric materials having a highly temperature-dependent spontaneous polarization. This property essentially occurs in so-called ferroelectric dielectric materials.
Generally pyroelectric radiation detectors comprise a plate capacitor, as indicated in FIG. 1 and whose dielectric material 2 is generally a monodomain ferroelectric monocrystal and which is consequently pyroelectric. The faces of the monocrystal in contact with the electrodes 4 of the capacitor are perpendicular to the polar axis N of the monocrystal.
The absorption of the incident radiation, particularly infrared radiation, on the surface or within the dielectric material leads to a temperature rise dT of the detector, which causes a variation dP.sub.s of the spontaneous polarization P.sub.s of the material. This leads to a voltage dV, which is applied to the input of a high impedance amplifier 6, e.g. constituted by a field effect transistor (FET).
Under these conditions of use the pass band-sensitized product increases in size in proportion to the ratio M=P/.epsilon.C. In this ratio, which appears as a quality factor, p is the pyroelectric coefficient of the dielectric material corresponding to the variation of the spontaneous polarization P.sub.s as a function of the temperature T, i.e.: ##EQU1## .epsilon. being the principal dielectric permittivity along the polar axis and C the calorific capacity of the material.
Hitherto an attempt has always been made to maximize the quality factor M either by acting on the chemical nature of the material leading to the exclusive use of ferroelectric materials, or more artificially by using composite structures. Such structures are described in the article appearing in the Journal Ferroelectrics no. 27, 1980, pp. 49 ff., by R. E. NEWNHAM, D. P. SKINNER, K. A. KLICKER, A. S. BHALIA, B. HARDIMAN and T. R. GURURAJA.
Thus, in the first case to obtain a maximum quality factor for a particular usage of a pyroelectric detector, it is necessary to carry out detailed research to determine the most suitable material. In the second case when composite structures are used, the major disadvantage is that it is difficult to obtain homogeneous detectors. This problem is particularly serious in imaging devices and particularly infrared imaging devices.
Moreover, the quality factor of the constituent material of known detectors is dependent on the temperature, so that the performances of these detectors are not stable with respect to operating temperature variations.